The present invention relates to a method for manufacturing a housing, or an insertion part for a housing, of a throttle valve connection piece. The housing comprises a throughflow opening in which a throttle or butterfly valve opens by pivoting about a pivot axis. The pivot axis extends transversely with respect to a longitudinal axis of the throughflow opening. The valve includes radial edges at its outer circumference. In a closed position, the valve, being in a throttle starting region, abuts an inner wall of a starting region, of the opening, at an abuttment region. The throttle starting region, which extends from the abutment region of the butterfly valve and along the inner wall of the throughflow opening in the direction of opening of the valve, may define a substantially spherical cap or circular cross section. The throttle starting region is displaced along a pivoted longitudinal axis of the throughflow opening. The inflow and outflow regions which adjoin the end of the throttle starting region on the inflow side and outflow side are formed so as to be cylindrical or so as to extend conically. The present invention further relates to a valve connection piece having a housing or insertion part of a housing which is manufactured according to the present method.
With such housings or insertion pieces for housings it is known to manufacture at least the throttle starting region in the direction of opening of the valve by means of metal-removing processing, owing to its complicated spherical cap-like or pivoted design. The spherical cap-like or pivoted design of the throttle starting region has the function of allowing the opening cross section which is cleared by the valve, as it opens out of the closed position, to increase only slowly in the throttle starting region, in order to permit sensitivity with respect to the throughflow of air in this region.
The method of manufacture of these known housings and insertion parts is very complex and does not make it possible to manufacture the housing or the insertion part from plastic.
WO-A-97/04259 has disclosed a method for manufacturing a housing or an insertion part for a housing of a butterfly valve connection piece, and a butterfly valve connection piece in which a core which is composed of four core parts is arranged in an injection molding mold and is encapsulated by means of injection molding. In each case, two core parts abutting one against the other with their end surfaces which face one another form a core separating plane at their adjoining end surfaces, the core separating planes of the two core part pairs extending in different planes. The two core part pairs are axially offset with respect to one another in such a way that steps which are set back radially are formed on the wall of the throughflow opening, with which steps the butterfly valve is in abutment in its closed position. At the junction between the wall of the throughflow opening and the radially set-back step a core separating burr is produced. Air eddies are generated in the vicinity of the butterfly valve both by the core separating burr and by the radially set-back steps with the result that the sensitivity with respect to the throughflow of air at the start of the opening of the butterfly valve is influenced in a disruptive fashion.